/
dft_ldos.cpp
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/
dft_ldos.cpp
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/* Copyright (C) 2005-2020 Massachusetts Institute of Technology.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "meep.hpp"
#include "meep_internals.hpp"
using namespace std;
namespace meep {
dft_ldos::dft_ldos(double freq_min, double freq_max, int Nfreq) {
freq = meep::linspace(freq_min, freq_max, Nfreq);
Fdft = new complex<realnum>[Nfreq];
Jdft = new complex<realnum>[Nfreq];
for (int i = 0; i < Nfreq; ++i)
Fdft[i] = Jdft[i] = 0.0;
Jsum = 1.0;
}
dft_ldos::dft_ldos(const std::vector<double> freq_) {
const size_t Nfreq = freq_.size();
freq = freq_;
Fdft = new complex<realnum>[Nfreq];
Jdft = new complex<realnum>[Nfreq];
for (size_t i = 0; i < Nfreq; ++i)
Fdft[i] = Jdft[i] = 0.0;
Jsum = 1.0;
}
// |c|^2
static double abs2(complex<double> c) { return real(c) * real(c) + imag(c) * imag(c); }
double *dft_ldos::ldos() const {
// we try to get the overall scale factor right (at least for a point source)
// so that we can compare against the analytical formula for testing
// ... in most practical cases, the scale factor won't matter because
// the user will compute the relative LDOS of 2 cases (e.g. LDOS/vacuum)
// overall scale factor
double Jsum_all = sum_to_all(Jsum);
double scale = 4.0 / pi // from definition of LDOS comparison to power
* -0.5 // power = -1/2 Re[E* J]
/ (Jsum_all * Jsum_all); // normalize to unit-integral current
const size_t Nfreq = freq.size();
double *sum = new double[Nfreq];
for (size_t i = 0; i < Nfreq; ++i) /* 4/pi * work done by unit dipole */
sum[i] = scale * real(Fdft[i] * conj(Jdft[i])) / abs2(Jdft[i]);
double *out = new double[Nfreq];
sum_to_all(sum, out, Nfreq);
delete[] sum;
return out;
}
complex<double> *dft_ldos::F() const {
const size_t Nfreq = freq.size();
complex<double> *out = new complex<double>[Nfreq];
sum_to_all(Fdft, out, Nfreq);
return out;
}
complex<double> *dft_ldos::J() const {
const size_t Nfreq = freq.size();
complex<double> *out = new complex<double>[Nfreq];
sum_to_all(Jdft, out, Nfreq);
return out;
}
void dft_ldos::update(fields &f) {
complex<double> EJ = 0.0; // integral E * J*
complex<double> HJ = 0.0; // integral H * J* for magnetic currents
double scale = (f.dt / sqrt(2 * pi));
// compute Jsum for LDOS normalization purposes
// ...don't worry about the tiny inefficiency of recomputing this repeatedly
Jsum = 0.0;
for (int ic = 0; ic < f.num_chunks; ic++)
if (f.chunks[ic]->is_mine()) {
for (src_vol *sv = f.chunks[ic]->sources[D_stuff]; sv; sv = sv->next) {
component c = direction_component(Ex, component_direction(sv->c));
realnum *fr = f.chunks[ic]->f[c][0];
realnum *fi = f.chunks[ic]->f[c][1];
if (fr && fi) // complex E
for (size_t j = 0; j < sv->npts; j++) {
const ptrdiff_t idx = sv->index[j];
const complex<double> A = sv->A[j];
EJ += complex<double>(fr[idx], fi[idx]) * conj(A);
Jsum += abs(A);
}
else if (fr) { // E is purely real
for (size_t j = 0; j < sv->npts; j++) {
const ptrdiff_t idx = sv->index[j];
const complex<double> A = sv->A[j];
EJ += double(fr[idx]) * conj(A);
Jsum += abs(A);
}
}
}
for (src_vol *sv = f.chunks[ic]->sources[B_stuff]; sv; sv = sv->next) {
component c = direction_component(Hx, component_direction(sv->c));
realnum *fr = f.chunks[ic]->f[c][0];
realnum *fi = f.chunks[ic]->f[c][1];
if (fr && fi) // complex H
for (size_t j = 0; j < sv->npts; j++) {
const ptrdiff_t idx = sv->index[j];
const complex<double> A = sv->A[j];
HJ += complex<double>(fr[idx], fi[idx]) * conj(A);
Jsum += abs(A);
}
else if (fr) { // H is purely real
for (size_t j = 0; j < sv->npts; j++) {
const ptrdiff_t idx = sv->index[j];
const complex<double> A = sv->A[j];
HJ += double(fr[idx]) * conj(A);
Jsum += abs(A);
}
}
}
}
for (size_t i = 0; i < freq.size(); ++i) {
complex<double> Ephase = polar(1.0, 2*pi * freq[i] * f.time()) * scale;
complex<double> Hphase = polar(1.0, 2*pi * freq[i] * (f.time() - f.dt / 2)) * scale;
Fdft[i] += Ephase * EJ + Hphase * HJ;
// NOTE: take only 1st time dependence: assumes all sources have same J(t)
if (f.sources) {
if (f.is_real) // todo: not quite right if A is complex
Jdft[i] += Ephase * real(f.sources->current());
else
Jdft[i] += Ephase * f.sources->current();
}
}
// correct for dV factors
Jsum *= sqrt(f.gv.dV(f.gv.icenter(), 1).computational_volume());
}
} // namespace meep